Electron gun assemblies for use in colour picture tubes

ABSTRACT

In an electron gun assembly for use in a colour picture tube wherein three electron guns are disposed in a regular triangular configuration, among a plurality of grid electrodes of the three electron guns those performing the same function for the electron beams are integrated into a single hollow cylindrical grid electrode and three electron beam transmission perforations arranged in a regular triangle are provided for one end wall of the hollow cylindrical grid electrode.

United States Patent 1 [111 3,889,146 Koizumi et al. June 10, 1975 ELECTRON GUN ASSEMBLIES FOR USE IN 2,726,348 12/1955 Benway 313L412 CO O PICTURE TUBES 2,752,520 6/1956 Morrell 313/412 3,772,554 11/1973 Hughes 313/412 [75] Inventors: Kihachiro Koizumi, Chiba; Yukihiro Izumida, Mobara; Yoshihiko y a M0baraan of Japan Primary Examiner-Siegfried H. Grimm Assignee: i, Ltd. Tokyo, Japan Attorney, Agent, or FlrmD1ke, Bronsteln,

Roberts, Cushman & Pfund [22] Filed: Mar. 6, 1974 [21] Appl. No.. 448,548 ABSTRACT Foreign Application Prim'ity Data In an electron gun assembly for use in a colour picture Aug. 29, 1973 Japan 48-96106 tube wherein three electron guns are disposed in a regular triangular configuration, among a plurality of [52] US. Cl 313/414; 313/D1G. 1 grid electrodes of the three electron guns those per- [51] Int. Cl. H01 j 29/50 forming the same function for the electron beams are [58] Field of Search 313/409, 412, 414, DIG. 1, integrated into a single hollow cylindrical grid elec- 313/413, 415-417 trode and three electron beam transmission perforations arranged in a regular triangle are provided for [56] References Cited one end wall of the hollow cylindrical grid electrode.

UNITED STATES PATENTS 2,690.51! 9/1954 Nicoll et a1. 313/412 6 Claims, 6 Drawing Figures ll] l ELECTRON GUN ASSEMBLIES FOR USE IN COLOUR PICTURE TUBES BACKGROUND OF THE INVENTION This invention relates to an electron gun assembly for use in a colour picture tube and more particularly to an improved construction of the grid electrode of a delta type electron gun assembly.

In the delta type electron gun assembly it is usual to dispose a first grid in front of the cathode electrode. The first grid is provided with a small opening having a diameter of from 0.6 to 1 mm at the center and applied with a negative potential with respect to the cathode electrode. In front of the first grid is disposed a second grid in opposed relation with respect to the first grid and a potential of from 200 to 400 volts is applied to the second grid for deriving out an electron beam from the cathode electrode. A third grid is disposed in front of the second grid with one end of the third grid contained in the second grid and the other end opposed to a fourth grid. A potential of from 4 to kilovolts is impressed upon the third grid whereas a potential of 20 to 27 kilovolts is impressed upon the fourth grid for focusing the electron beam on a shadow mask.

For the purpose of preventing an electric discharge due to high voltage, the ends of the second, third and fourth grids are provided with peripheral beads and these grids are secured to glass bead supports, which in turn are mounted on a glass plate for supporting the electron gun assembly. Each of three electron guns is inclined about 1 with respect to the tube axis so that three electron beams emitted by the guns converge at one point of the shadow mask. I

In this manner, as it is necessary to correctly arrange respective electrodes of each gun and to correctly support on the glass bead supports respective electron guns such that each of them incline about 1 with respect to the tube axis, it is necessary to assemble the electron gun assembly at a considerable high accuracy, thus rendering difficult the assembling operation.

In the electron gun assembly for use in a colour picture tube and having a construction as described above, there is a problem regarding the resolution of the received picture. For the purpose of improving the resolution it has been the practice to decrease the magnifying power of the tube and to decrease the spherical aberration of the main electron lens formed by the third and fourth grid electrodes. Although these conditions can be fulfilled by increasing the diameter of the main electron lens, the diameter of the main electron lens is limited by the peripheral beads formed on ends of the electrodes, the inclination angle of the electron guns, and the dimension of the glass bead. This is also related to the diameter of the neck of the tube. For example, for a colour picture tube with a deflection angle of 1 and a neck diameter of 29mm, the diameter of the electron lens is decreased to 70% of that of a tube having electron lens so that it has been difficult to improve the LII a deflection angle of 90 and a neck diameter of 36mm,

resolution.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide an improved electron gun assembly for use in a colour picture tube capable of improving the resolution of the reproduced picture.

Another object of this invention is to provide an improved electron gun assembly for use in a colour picture tube which can be readily assembled at high accuracies.

Still another object of this invention is to provide an improved electron gun assembly for use in a colour picture tube capable of reducing the spherical aberration of the electron lens and reducing the variations of the beam spot position on the fluorescent screen, of the raster shift and of the initial drift of the convergence.

According to this invention, these and further objects can be accomplished by providing a delta type electron gun assembly for use in a colour picture tube comprising cathode electrodes which are arranged in a regular triangular configuration, a hollow cylindrical grid electrode disposed to confront the cathode electrodes and extending substantially coaxially with the tube in the direction of travel of the electron beams emanated by the cathode electrodes, the grid electrode being provided with three electron beam transmission perforations through one end wall thereof. These electron beam transmission perforations are also arranged in a regular triangular configuration.

BRIEF DESCRIPTION OF THE DRAWINGS Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a side view, partly broken away, of a prior art delta type electron gun assembly;

FIG. 2 is an end view of the electron gun assembly shown in FIG. 1',

FIG. 3 is a side view of one embodiment of the electron gun assembly constructed in accordance with this invention and utilized in a colour picture tube;

FIG. 4 is an end view of the electron gun assembly shown in FIG. 3',

FIG. 5 is a partial sectional view taken along a line VV in FIG. 4; and

FIG. 6 is a partial sectional view taken along a line VIVI in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIGS. 1 and 2, in a prior art delta type electron gun assembly, each electron gun 3 comprises a cathode electrode 9, a first grid electrode 10, a second grid electrode 11', a third grid electrode 12', and a fourth grid electrode 13' which are mounted on a glass plate 16 by glass bead supports 15, respectively. The ends of the second to fourth grid electrodes are provided with peripheral beads 14 for the purpose of preventing high voltage discharge. In such an electron gun assembly for use in a colour picture tube having a deflection angle of 1 10 and a neck diameter of 29mm,

it is usual to use a ratio of the diameter D of electron gun grid, as measured at the end of the fourth grid confronting the fluorescent screen, to the distance 8,, be-

tween the tube axis and respective gun axis of up to D/S =l.35. More particularly. when S =4,72mm, the diameter D of the third and fourth grid electrodes 12 and 13 is selected to be 6.35mm, and when S =5.6mm. D=7.6mm.

A preferred embodiment of the electron gun assembly of this invention shown in FIGS. 3 to 6 comprises three first grid electrodes 10 arranged in a delta, three second grid electrodes 11 also arranged in a delta and disposed in front of the first grid electrodes, and a third hollow grid electrode 12 having a cross-sectional configuration of a regular triangle. Three axial projections 17 disposed on the apices of a regular triangle are formed on one end of the third grid electrode 12 to confront respective second grid electrodes 11. Each projection 17 is provided with a central aperture for transmitting the electron beam. Three perforations are formed through the end wall of the third grid electrode 12 which confronts the fourth grid electrode 13 at positions corresponding to the perforations of the projections 17. The third grid electrode 12 is formed by bonding together two halves of semicircular metal plates. The fourth grid electrode 13 is also a cylindrical body having a cross-sectional configuration of a regular triangle, and its end wall confronting the third grid electrode 12 is also provided with three perforations 21 corresponding to the three perforations 20 of the third grid electrode 12. The convergence of the electron beams is accomplished by a displaced electron lens which is formed by outwardly displacing the perforations 21 provided for the fourth grid 13 by about 0.1 to 0.2 mm with respect to the perforations 20 provided for the third grid electrode 12, or by providing a suitable convergence yoke, not shown. As shown in FIG. 6 perforations 20 and 21 provided for the confronting end walls of the third and fourth grid electrodes 12 and 13 are provided with inwardly curved and axially extending peripheral edges 18 and 19. As shown the third and fourth grid electrodes 12 and 13 are arranged substantially coaxial. With this construction, as can be noted from FIGS. 5 and 6, even when the distance S between the axis of respective perforation 20 and the tube axis is selected to be 4.72 mm as in the prior art design it is possible to make the inside diameter D of the grid perforation to be equal to from 7.0 to 7.7 mm which is larger than 6.35 mm of the electron gun grid diameter of the prior art design thus increasing the ratio D/S to a value of from 1.48 to 1.63. It is considered that this is attributable to the following ground. More particularly, the spacing 1 between two adjoining perforations 20 provided for the third control grid electrode 12 is determined by the inwardly and axially extending curved portion 19 that defines the perforation 20 as can be noted from FIG. 6, so that it is possible to make larger the diameter D than the prior art construction in which bead 14 is formed on the outer periphery of the grid electrode 12'.

Moreover, as it is possible to correctly converge the electron beams by means of a displaced electron lens which is formed by the difference in the high potentials impressed upon the third and fourth grid electrodes instead of inclining the axis of each electron gun with respect to the tube axis, it is possible to eliminate such defects as the electric discharge and increase in the stray capacitance which are caused by the decrease in the distance between the rear end of the electron gun assembly, that is the end thereof facing to the cathode electrode and the inner wall of the neck of the tube.

As described hereinabove, according to the improved construction of this invention it is possible to increase the ratio D/S beyond 1.45 thus decreasing the spherical aberration of the main electron lens. More over, as it is possible to design the third grid electrode as an integral construction having a large length, it is possible to improve the resolution by 20 to 30% over the prior art construction. Further, as the grid electrodes applied with the same potential are united into an integral structure, and since respective electron guns are arranged substantially coaxial with the tube axis it is possible to readily fabricate the electron gun assembly at higher accuracies. Improvement of the accuracy of the fabrication also decreases the variations of the position of the electron beam spot on the fluorescent screen, of the raster shift and of the initial drift of the convergence.

Although in the foregoing embodiment each of the third and fourth grid electrodes was shown as an integral structure, it is also possible to construct the other grid electrodes (that is the first and second grid electrodes) also as integral structures.

Although, in the above described embodiment, the electron gun assembly was shown as of a bipotential type, it should be understood that the invention is also applicable to the electron gun assembly of the unipotential type.

Also, instead of disposing three electron guns on the apices of a regular triangle the configuration of the triangle may be different provided that the object of this invention can be accomplished.

What is claimed is:

l. A delta type electron gun assembly for use in a colour picture tube comprising cathode electrodes arranged in a regular triangular configuration, first grid electrodes disposed in front of said cathode electrodes respectively, second grid electrodes disposed in front of said first grid electrodes respectively, a third hollow cylindrical grid electrode disposed to confront said second grid electrodes and extending substantially coaxially with said tube in the direction of travel of the electron beams emitted by said cathode electrodes, said third grid electrode being provided with three electron beam transmission perforations through one end wall far from said cathode electrodes thereof, said three perforations being also arranged in a regular triangular configuration, a fourth cylindrical grid electrode dis posed in front of said third grid electrode, said fourth grid electrode being also provided with three electron beam transmission perforations arranged in a regular triangular configuration through a wall facing to said one end wall thereof, said third and fourth cylindrical grid electrodes comprising members for forming a main electron lens by applying different potential thereon, and means for supporting said cathode electrodes and said grid electrodes.

2. The electron gun assembly according to claim 1 wherein said third hollow cylindrical grid electrode has substantially regular triangular cross-sectional configuration.

3. The electron gun assembly according to claim 1 wherein said electron beam transmission perforations through said one end wall of said third grid electrode are circular and are dimensioned to satisfy a relation D/S L45, where D represents the inside diameter of wall on the side opposite to said one end wall, and said three projections are also arranged in a regular triangular configuration corresponding to said electron transmission perforations.

6. The electron gun assembly according to claim 1 wherein said electron beam transmission perforations of the fourth control grid electrode are displaced outwardly with respect to those of the third control grid electrode. 

1. A delta type electron gun assembly for use in a colour picture tube comprising cathode electrodes arranged in a regular triangular configuration, first grid electrodes disposed in front of said cathode electrodes respectively, second grid electrodes disposed in front of said first grid electrodes respectively, a third hollow cylindrical grid electrode disposed to confront said second grid electrodes and extending substantially coaxially with said tube in the direction of travel of the electron beams emitted by said cathode electrodes, said third grid electrode being provided with three electron beam transmission perforations through one end wall far from said cathode electrodes thereof, said three perforations being also arranged in a regular triangular configuration, a fourth cylindrical grid electrode disposed in front of said third grid electrode, said fourth grid electrode being also provided with three electron beam transmission perforations arranged in a regular triangular configuration through a wall facing to said one end wall thereof, said third and fourth cylindrical grid electrodes comprising members for forming a main electron lens by applying different potential thereon, and means for supporting said cathode electrodes and said grid electrodes.
 2. The electron gun assembly according to claim 1 wherein said third hollow cylindrical grid electrode has substantially regular triangular cross-sectional configuration.
 3. The electron gun assembly according to claim 1 wherein said electron beam transmission perforations through said one end wall of said third grid electrode are circular and are dimensioned to satisfy a relation D/S0 > or = 1.45, where D represents the inside diameter of said perforations and S0 the distance between the centers of said perforations and the axis of said tube.
 4. The electron gun assembly according to claim 1 wherein each of said perforations through said one end wall of said third grid electrode is provided with an inwardly and axially curved periphery extending toward said cathode electrodes.
 5. The electron gun assembly according to claim 1 wherein said third hollow cylindrical grid is provided with three perforated cylindrical projections on the end wall on the side opposite to said one end wall, and said three projections are also arranged in a regular triangular configuration corresponding to said electron transmission perforations.
 6. The electron gun assembly according to claim 1 wherein said electron beam transmission perforations of the fourth control grid electrode are displaced outwardly with respect to those of the third control grid electrode. 